Integrated circuit for power supply and power supply system

An integrated circuit for a power supply that is connected to an AC power supply via an input circuit including a capacitor, comprising:

• a voltage dividing unit that divides an input voltage to generate a divided voltage;
• a shutoff detection unit that compares the divided voltage with a predetermined reference voltage to detect shutoff of the AC power supply;
• and
• a discharge unit that pulse-discharges accumulated charge in the capacitor in pulses when shutoff of the AC power supply is detected,
• wherein the voltage dividing unit sets a ratio of the divided voltage to the input voltage to a first voltage division ratio when no shutoff of the AC power supply is detected, and sets a ratio of the divided voltage to the input voltage to a second voltage division greater than the first voltage division ratio when shutoff of the AC power supply is detected, and
• wherein when the shutoff detection unit outputs an output signal to the voltage dividing unit and the discharge unit, the voltage dividing unit changes the ratio of the divided voltage to the input voltage from the first voltage division ratio to the second voltage division ratio according to the output signal, and the discharge unit pulse-discharges accumulated charge in the capacitor in pulses according to the output signal.